Many industrial applications utilize air operated hoist systems to enable loads to be lifted. Air hoists are equipped with air motors which are sized to provide a specific maximum lifting capacity (i.e., ¼ Ton, ½ Ton, 1 Ton, etc.). The hoist controls typically control the vertical movement of the lifting mechanism. When in a lifting mode, the hoist will have the capability to lift up a predetermined rated lift capacity.
Many applications require a tool or lifting device, suspended from the hoist to engage the load. These devices are called “End-Effectors” or “Below the Hook Tooling”. It is very common for the end-effector tooling and load to weigh less than the rated lifting capacity of the air hoist. Therefore, excess capacity remains for the hoist to lift a greater load. This can create an unsafe environment in many industrial applications.
Examples of safety related issues may be:
1. Attempting to lift heavier objects than the rated capacity of the end-effector tool, which may be less than the hoist. The hoist could continue to lift and the tool be placed in an unsafe condition. A further problem may occur wherein the hoist applies a maximum lift force against a load to be lifted, where the load is too heavy for the hoist to lift. Upon removing the load from the hoist, the hoist may continue to supply the maximum lift force, causing the end-effector tool to abruptly lift upward with the maximum lift force, possibly damaging equipment, tooling, or placing the operator in an unsafe situation.
2. The tool and/or load contacting an obstacle such as an adjacent shelf or a machine component. The hoist may have the lifting capacity to continue an upward movement possibly damaging equipment, tooling, or placing the operator in an unsafe situation.
It is an object of the present invention to produce a pneumatically operated hoist system which is capable of sensing an overload and preventing any further flow of the supply of pressure operating fluid.